There is a surgical mobile C-arm unit including an imaging unit that contains an X-ray source and an X-ray detector as well as two units of monitors to display images sent from the X-ray detector.
The surgical mobile C-arm unit includes a circular X-ray detector using I.I. (Image Intensifier) and a square X-ray detector using FPD (Flat Panel Detector). An image direction toward an object rotates by rotating both the detectors with an imaging unit parallel to the horizontal surface.
As a method to keep an image orientation constant, PATENT LITERATURE 1 discloses a method to keep a detector itself in a certain direction by balancing out rotation amounts of the C-arm and the detector.